This invention relates to slurry compositions for ground improvement using blast-furnace slag cement and a method of producing soil cement slurry by using such slurry compositions.
In recent years, the demand for reducing the emission rate of carbon dioxide and improving efficient energy consumption is becoming increasingly stronger. Under this condition, blast-furnace slag as by-product from steel mills is being effectively used as material for blast-furnace slag cement in the form of blast-furnace slag fine particles in mountain stationary construction, underground water stop construction and soft ground improvement construction works. Generally, when such a ground improvement work is carried out, cement slurry with a mixture of cementatious stabilizer and water (cement milk) is injected into the ground and a drilling and kneading machine is used to mix and stir it with the ground at the site, and blast-furnace slag cement is used here as the cementatious stabilizer. Blast-furnace slag cement is usually produced by mixing blast-furnace slag fine particles into normal portland cement and is usually divided according to the JIS-R5211 standard into the following three kinds, depending on the amount of the blast-furnace slag fine particles: Type A (over 5% to 30%), Type B (over 30% to 60%) and Type C (over 60% to 70%). Type B with a good balance in characteristics is usually used when actual ground improvement is done.
For ground improvement, Type B blast-furnace slag cement is normally mixed into 1 m3 of ground at a rate of 100-400 kg, but since about 400 kg of carbon dioxide is emitted for producing 1 ton of Type B blast-furnace slag cement, this means that 40-160 kg of carbon dioxide is emitted for improving 1 m3 of ground by using Type B blast-furnace slag cement, exclusive of the emission of carbon dioxide generated by the operation of construction machines, transportation of materials, etc. For this reason, in the field of carrying out ground improvement, there have been demands for the development of technology for suppressing the generation of carbon dioxide by using blast-furnace slag cement at a higher rate, while maintaining workability and the prerequisite that the ground to be improved gain the necessary strength.
The present invention relates to slurry compositions for ground improvement using blast-furnace slag cement that can respond to such demands, as well as a method of producing soil cement slurry using such compositions.
Regarding the effects of the conventional use of portland cement for ground improvement, it has been reported, for example, in “Manual for Ground Improvement by Cementatious Stabilizer” (1984) pages 42-44, edited by the Cement Association of Japan, that portland cement is alkaline because calcium hydroxide is generated when it comes into contact with water and, if it is used for ground improvement, the pH of the ground increases up to 10, adversely affecting the growth of plants, etc. and that, if portland cement is used for improving ground with low water content such as a loamy layer, it becomes easier for hexavalent chromium in the portland cement to elute, adversely affecting the environment. Besides the above, there have been proposals for the improvement of fluidity of cement slurry used for ground improvement such as those in Japanese Patent Publications Tokkai 11-256161, 2000-169209 and 2006-298726, as well as for hydraulic compositions using blast-furnace slag, etc. usable also for ground improvement such as those in Japanese Patent Publications Tokkai 62-158146, 63-2842, 1-208354, 10-114555 and 2002-241152, but there have been no detailed reports or proposals contributing to the reduction in emission of carbon dioxide.